Proton exchange membrane water electrolysis (PEMWE) faces efficiency degradation as increased current density leads to bubble accumulation, which reduces the active reaction area. To investigate this phenomenon, an analysis of bubble dynamics is required. This study proposes a method that sequentially utilizes nnU-Net for segmentation and You Only Look Once (YOLO) for key point extraction. The analysis is performed by identifying concave points as geometric landmarks to distinguish individual bubbles. This framework enables the characterization of flow patterns during PEMWE operation. Experimental results showed that the average number of bubbles in the upstream channel (2^nd channel) slightly increased before declining, while it consistently decreased in the downstream channel (10^th channel). The void fraction increased with current density regardless of the channel location. This study provides fundamental data for analyzing two-phase flow characteristics in water electrolysis systems.

This study presents a multi-fidelity fluid-structure interaction (FSI) framework to investigate tissue deformation and hemodynamic responses during cuff-based blood pressure measurement. The approach couples one-dimensional deformable blood flow equations with the three-dimensional Cauchy equation of motion, enabling efficient simulation of vascular-tissue interactions under external pressure. An idealized cylindrical upper-arm model including an artery and a vein was constructed to examine the biomechanical behavior during cuff inflation and deflation. The results show that flow and pressure responses change markedly as the applied external pressure exceeds systolic blood pressure, leading to a rapid reduction and eventual cessation of blood flow. Distinct responses were observed between the artery and vein, accompanied by spatially heterogeneous vessel deformation. These findings demonstrate that the proposed multi-fidelity FSI framework provides an efficient and robust computational tool for capturing the key biomechanical responses underlying cuff-based blood pressure measurement and offers potential for future patient-specific modeling and device optimization.

Conventional liquid shutters are often limited by low interfacial stability against external disturbances. To overcome this limitation, this paper proposes a novel EWOD-based bistable liquid shutter incorporating barrier structures designed for robust light blocking in dynamic environments. By inducing a Laplace pressure gradient, this configuration facilitates bistability without continuous power input. This study demonstrates three key contributions through experimental characterization. First, the introduced barrier structure successfully induces bistability, significantly enhancing energy efficiency. Second, the device achieves high optical contrast, exhibiting a low transmittance of 1.7% at 120 Vrms. Third, vibration experiments reveal the critical role of barrier height in mechanical robustness: while lower barrier structures fail under external acceleration, a 100 ㎛-high barrier maintains interfacial integrity even at an acceleration of 347.5 m/s². The proposed bistable shutter, offering superior mechanical robustness, holds significant potential for diverse applications, ranging from camera modules in mobile electronics to next-generation optical systems.

We numerically investigate sloshing in a partially filled rectangular tank and develop a mechanical equivalent model for low-order dynamic representation. The two-phase flow is computed with the volume-of-fluid method in OpenFOAM. A horizontally oscillating tank is considered to examine the resonant free-surface response, center of mass motion and the suppression effect of rigid baffles. The results reveal that the maximum center of mass elevation occurs near, but not exactly at, the linear first natural period because of nonlinear soft-spring behavior. Rigid baffles mitigate free-surface deformation and reduce the resonant response, with a stronger reduction for a higher baffle. The equivalent sloshing mass, stiffness and damping are identified from free-decay and sudden-stop simulations. The predicted natural frequency and sloshing mass agree well with linear theory, demonstrating the potential of developing an equivalent mechanical model based on high-fidelity simulation data.

We experimentally investigates the reconfiguration and falling dynamics of freely falling kirigami sheets in a low-Reynolds-number regime. During free fall, the kirigami sheet reconfigures due to an equilibrium of forces. We found that this reconfigured shape strongly depends on the sheet thickness, which dictates its bending stiffness. Based on high-speed image and processing, we quantified the structural deformation and terminal velocity. Results indicate that when the cutting lines successfully transition into holes, greater structural deformation correlates with a higher terminal velocity. Notably, if the sheet thickness exceeds a critical threshold, the bending stiffness prevents the cutting lines from holes. This causes a drastic geometric shift, temporarily increasing the terminal velocity. These mechanical insights into design parameters provide a foundation for developing drag-based micro-transporters.

This study investigated the temporal evolution of surface bubbles on pristine and plasma-etched PTFE under recirculating water-channel flow. Plasma etching increased the water contact angle from 116±1° to 170±1° and reduced the sliding angle to approximately 1°. Top-view images were acquired for 1 h at 20 s intervals and processed to determine the bubble count and mean equivalent diameter. On the plasma-etched surface, the bubble count increased initially and then remained within a narrow range, while the mean equivalent diameter stayed near 0.47 mm. In contrast, the pristine surface showed a progressive decrease in bubble count accompanied by an increase in mean equivalent diameter. The count-diameter plot showed a compact upper-right cluster for the plasma-etched surface and a broad negative trend for the pristine surface. These results indicate that, under the present flow condition, plasma etching favors the retention of a bubble population characterized by a relatively high count and large mean equivalent diameter.

This study investigated the free-surface wake flow behind a circular cylinder under regular waves using particle image velocimetry (PIV). A cylinder (D = 0.114 m) was installed in an 18 m-long, 1.2 m-wide wave flume with a water depth of 0.6 m. Four wave heights (H = 0.037, 0.111, 0.185, and 0.259 m) were tested at a fixed wave period (T = 1.2 s). In the wake, u*_RMS was lowest near the cylinder and increased downstream, with the most rapid recovery at x/D = 0.0-0.5, whereas w*_RMS varied little with x/D. At a given x/D, both u*_RMS and w*_RMS decreased with increasing wave height, indicating stronger wake distortion. Near the cylinder surface, alternating positive and negative vorticity appeared with the incident-wave period, with peak magnitudes near θ = π/2 and 3π/2. The dimensional ω_RMS increased with wave height and decreased nearly linearly with depth below the free surface, whereas the normalized ω*_RMS remained nearly constant with depth and decreased as wave height increased. These results show that, under the tested regular-wave conditions, the depthwise distribution of wake vorticity is closely related to the incident-wave velocity gradient.